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Spoiled with Sunshine -- a delightful "Omega Block"
Submitted by Tim Buckley on Thu, 11/11/2010 - 9:28am.
You'll be hard pressed to find anyone that's not in love with this weather. But why has it been so nice for so long? It's all thanks to a pattern in place we meteorologists refer to as an "Omega Block".
It may sound a bit more complex and technical than it actually is - but simply put, an "Omega Block" is a weather pattern that takes the shape of the Greek letter Omega. If you look at the current path of the Jet Stream on the map above, you can see that it resembles a capital Omega. Inside the Omega - especially towards the top - we find an abnormally strong area of high pressure which is typically colder than normal. Outside of the Omega we find large troughs of low pressure which serve as the path for storm systems to be deflected around the high pressure.
The reason why it's called a "block", is that these patterns typically remains nearly stationary for several days to even weeks at a time, "blocking" the movement of weather systems. The high pressure in the center is the stubborn force behind the block. The strong High plants itself in an area and doesn't budge. Approaching storms have no choice but to be deflected around the high, and can even themselves become stationary on the periphery. This might be opposite than what you'd expect. Shouldn't strong storms be able to push the high out of the way? After all, they bring nasty weather, which should be able to push out nothing but sunshine! It's actually the opposite.
I had a meteorology professor at Penn State that always used to say, "Cold air goes where it wants." We all know that cold air is more dense than warm air, the same reason why warm air will rise up through your house and cold air will sink to the bottom. Centers of high pressure are made of relatively cold, dense air at their core. Low pressure centers are the opposite. So - centers of high pressure are often the driving force behind the movement of weather systems.
In this case, the high is so incredibly strong that it's deflecting anything coming in contact with it. Storms have no choice but to go all the way up and around the system, or even simply stall out. Until the high budges, the block will remain in place. On the ground, this means that your weather isn't going to change with a block ongoing. This can be good -- or bad. Luckily for us, we're in the middle of the Omega.
Looking at the map above you can see our position inside the block is a good one. We're in the stationary high pressure zone which means nice weather for us. Being on the East side of the high, we've been a bit cooler than normal. On the opposite side of the high, areas have been running well above normal - which is what we'd expect in this pattern. Outside of the Omega, unsettled and dreary weather is usually the rule. Storm systems can become stalled out overhead and mean for a very long string of miserable days. Again, lucky for us we're in the clear!
We're already about a week into this pattern, so the question now is how long can it last? It looks like quite a bit longer. Looking ahead to this weekend, a storm system in the Central Plains will become the next victim of "the block", getting deflected around the system to the north. You can see below on the GFS Model forecast for Friday morning that the blocking High is still firmly in control along the East Coast.
After this storm system dissolves and heads off to the north around the High, another stronger trough will build in behind it. Looking at the map below you can see the GFS is forecasting that the blocking High on the East Coast has finally departed by early next week, allowing this huge monster trough to move in from the west and sweep across the country.
This next storm will be the one that finally brings an end to our string of sunny days. But I think 10-12 days of sunshine is long enough - it gets a little monotonous for us forecasters after a while! (Even if the weather itself is beautiful)
Behind this huge trough sweeping across the country, the early indications are that bitterly cold Arctic air will begin to mobilize in Canada and try to move itself on southward toward the end of November - perhaps in time for Thanksgiving. Stay tuned for more details there!
That's all for now. Enjoy the gorgeous weather here on this Veterans Day. If you are a Veteran, thank you for your service!
By: Tim Buckley